Enamel Prisms Research Articles

ASPECTS OF SURFACE ENAMEL MINERALIZATION IN PERMANENT TEETH OF CHILDREN FROM DIFFERENT AGE GROUPS

The purpose of our study was the examination of external surface enamel mineralization in permanent teeth of children from different age groups. We examined sections of 50 extracted for orthodontic indications premolars in patients from different age groups. A study of 16 teeth was conducted in 11-13 years old children, 8 teeth were investigated in each group of 13-15 years old, as well as 9 teeth in 15-16-year-old patients. All patients were appointed with remineralization therapy during the first six months after tooth eruption fallowed by application of “Tooth Mousse” ones a day for 2 weeks every six months with appropriate monitoring. The comparison group, on the other hand, consisted from extracted teeth taken from children who were not subjected to any preventive remineralization measures. The distribution by age and the studied material was identical to the main group. Segmentation of the teeth was carried out after the tooth extraction with separation of the crown structure and further polishing of the crown using polishing brushes without pastes. Sections 0.3-0.5 mm thick were formed with a diamond disc. The enamel samples were cleaned and degreased and then examined in a polarizing microscope (Optika B-150POL-B 40x-640x Bino) at a magnification in 500 times. The description of the enamel microscopic surface was carried out according to the following parameters: surface heterogeneity, surface opaqueness/shininess, surface roughness/smoothness. The surface homogeneity was assessed by calculating the ratio of identified surface areas that visually differed from the overall enamel texture, which was characteristic of the predominant investigated surface enamel. There were criteria for evaluating the enamel surface heterogeneity according to the research data in a polarizing microscope : the presence of numerous well-defined cracks, the visualization and number of areas from which the enamel prisms extend, the presence and number of enamel surface irregularities confirmed by a change in the direction of the light beam, the percentage of surface homogeneity, which was calculated as the ratio of the area of ​​the visually homogeneous enamel surface to the area with ​​any microscopically detected changes. To assess the opacity of the enamel surface by the microscopic polarization study, the criteria of visual assessment of shiny and dark areas of interest were used. The study suggested that microscopic changes are characterized by a decrease of total number in enamel surface irregularities and an increase of its glossiness and smoothness at the approach of structural compositional stabilization at 15-16 years. The analysis also revealed that there were marked microscopic differences observed in enamel of 15-16 years old after remineralization with the "Tooth Mousse" gel and a comparison group (without remineralization therapy).The difference between them is reliable (p<0.01) according to the indicators of the relative average level of surface heterogeneity, and also statistically different from similar indicators that were registered in the age groups 11-13 and 13-15 years old (p<0.01). The gained results can be considered as the expediency grounds for implementation of dental caries prevention at the early stages of secondary mineralization (immediately after eruption) and throughout the entire period of its intensive phase, which will further contribute to the stabilization of the caries-resistant enamel.

Comparing the remineralization potential of undemineralized dentin powder versus chicken eggshell powder on artificially induced initial enamel carious lesions: an in-vitro investigation

BackgroundWhite spot lesions are a widespread undesirable effect, especially prevalent during fixed orthodontic treatments. The study compared the in vitro enamel remineralization potential of undemineralized dentin matrix (UDD) versus chicken eggshell powder (CESP) for artificially induced enamel lesions.Methods100 caries-free and sound maxillary premolars were randomly divided into four groups each contain 25 teeth: Group I (Baseline): No treatment was done to the enamel surface. Group II (Negative control ): The enamel surface of the teeth underwent demineralization using demineralizing solution to create artificial carious lesions then kept in artificial saliva. Group III (CESP treated): After demineralizing the tooth surface, the teeth have been suspended in the CESP remineralizing solution. Group IV (UDD treated): After enamel demineralization, the teeth were suspended in UDD remineralizing solution. The remineralization potential was assessed by Vickers microhardness testing, scanning electron microscopic examination (SEM), and energy dispersive X-ray (EDX).ResultsThe current study demonstrated an increase in the mean microhardness of CESP and UDD-treated groups; however, It was nearer to the baseline level in the UDD group. SEM imaging revealed greater enamel remineralization in the UDD group compared to the remaining groups. The UDD group disclosed complete coverage for the prismatic enamel compared to the CESP group, which revealed a partially remineralized enamel surface. Interestingly, the Ca/P ratio increased significantly in the CESP group compared to the negative control group. In contrast, a higher significant increase in the mean Ca/P ratios was recorded in the UDD group compared to the test groups.Conclusionbiomimetic UDD and CESP powder should be utilized to treat enamel early carious lesions. However, UDD demonstrated the most significant remineralization potential.

The effects of beverage erosion on enamel: evaluating surface characteristics and loss of calcium and phosphate ions

BackgroundThe erosive impacts of various beverages on dental enamel have been identified as a potential erosive threat to dental hard tissues. This in vitro study aimed to address this by utilizing a systematic approach and advanced analytical methods to study enamel erosion due to selected beverages in a simulated oral environment.MethodsForty-nine extracted sound second premolar teeth were collected, disinfected, and prepared. These teeth were randomly allocated into seven groups, each exposed to a different beverage: distilled water, mineral water, instant coffee, black tea, Pepsi-Cola, orange juice, and synthetic vinegar. The modified Nordini Artificial Model (mNAM) was used to simulate the oral cavity. The enamel surfaces were scanned using a Scanning Electron Microscope (SEM) and analyzed using Energy-Dispersive X-ray Spectroscopy (EDS). Surface hardness was measured using the Knoop Hardness Scale. Statistical analysis was conducted using the Wilcoxon signed-rank test, with a significance level set at p < 0.05.ResultsDistilled water and mineral water exhibited no significant changes in enamel surface or hardness. Coffee caused an 8–9% loss of calcium and phosphate, indicating potential erosion. Black tea showed signs of remineralization rather than demineralization. Pepsi-Cola and orange juice caused substantial erosion, with Pepsi-Cola resulting in a nearly 24% loss of calcium. Vinegar had a marked erosive effect, with a 17% loss of both calcium and phosphate. SEM images corroborated these findings, showing pronounced enamel prisms and increased visibility of minor cracks in post-treatment teeth. EDS analysis revealed significant changes in the elemental composition of the enamel.ConclusionsThis study categorised beverages based on their pH and fluoride content, revealing that drinks like Pepsi-Cola and orange juice are acidic but low in fluoride, whereas black tea, mineral water, and vinegar are acidic yet contain fluoride. The study suggests that the decrease in pH of acidic beverages may contribute to dental erosion, with fluoride as a mitigating factor. Among the various metrics assessed for evaluating dental erosion, hardness emerged as the most reliable quantitative parameter.

Study of hard tissues of the tooth crown using scanning electron microscopy and elemental analysis

The introduction of new methodological approaches actualizes research that makes it possible to establish relationships between the elemental composition of hard dental tissues and microscopic analysis data. Using scanning electron microscopy, the nature of the location and size of enamel prisms was revealed, and a description of the structure of the initial and final enamel was given. The zone of the dentino-enamel junction, the location of the dentinal tubules and the composition of the dentin matrix were studied. It has been proven that the content of water, organic matter, sodium and potassium is higher in dentin, and the concentration of magnesium, phosphorus and calcium is higher in enamel.

Roles of the histone methyltransferase SET domain bifurcated 1 in epithelial cells during tooth development

ObjectiveThis study aimed to reveal the effects of SET domain bifurcated 1 (SETDB1) on epithelial cells during tooth development. DesignWe generated conditional knockout mice (Setdb1fl/fl,Keratin14-Cre+ mice), in which Setdb1 was deleted only in epithelial cells. At embryonic day 14.5 (E14.5), immunofluorescence staining was performed to confirm the absence of SETDB1 within the epithelium of tooth embryos from Setdb1fl/fl,Keratin14-Cre+ mice. Mouse embryos were harvested after reaching embryonic day 13.5 (E13.5), and sections were prepared for histological analysis. To observe tooth morphology in detail, electron microscopy and micro-CT analysis were performed at postnatal months 1 (P1M) and 6 (P6M). Tooth embryos were harvested from postnatal day 7 (P7) mice, and the epithelial components of the tooth embryos were isolated and examined using quantitative RT-PCR for the expression of genes involved in tooth development. ResultsSetdb1fl/fl,Keratin14-Cre+ mice exhibited enamel hypoplasia, brittle and fragile dentition, and significant abrasion. Coronal sections displayed abnormal ameloblast development, including immature polarization, and a thin enamel layer that detached from the dentinoenamel junction at P7. Electron microscopic analysis revealed characteristic findings such as an uneven surface and the absence of an enamel prism. The expression of Msx2, Amelogenin (Amelx), Ameloblastin (Ambn), and Enamelin (Enam) was significantly downregulated in the epithelial components of tooth germs in Setdb1fl/fl,Keratin14-Cre+ mice. ConclusionsThese results indicate that SETDB1 in epithelial cells is important for tooth development and clarify the relationship between the epigenetic regulation of SETDB1 and amelogenesis imperfecta for the first time.

Morphological features of enamel in fluorosis of different degrees of severity

The occurrence of dental fluorosis is facilitated by a violation of enamel mineralization caused by fluorides, which enter the human body in excess during its development and formation and have a toxic effect on enamel blasts. However, the molecular mechanisms involved in the pathogenesis of fluorosis are not fully understood. Enamel formation is a complex process involving cell proliferation and differentiation through epithelial-mesenchymal sequential secretion of matrix proteins, tissue-specific transport of ions including calcium and fluoride, and precipitation and alignment of enamel crystals through interactions between organic and inorganic molecules. Understanding the morphological features of enamel changes during fluoride intoxication of the human body in the endemic region allows us to clearly understand the need for a comprehensive solution to this medical and social problem. The aim was to study the morphological features of enamel in fluorosis in residents of the endemic region of Ukraine, in particular the Poltava region. The work examines different groups of teeth (both intact and affected by fluorosis) removed for orthodontic or clinical indications in men and women aged 17 to 40 years. Morphological signs were studied first on native, and later on histochemically stained sections. It was established that the violation of the structure of the enamel layer of the teeth in mild and severe fluorosis is characterized by both partial and complete violation of the movement of the enamel prisms with signs of destruction. Fragmentation and homogeneity throughout the entire thickness were found in some areas of the enamel. When evaluating histochemically stained sections of teeth affected by fluorosis, it was established that dystrophic changes in the enamel structure and accumulation of acidic glycosaminoglycans in the lesions are more characteristic of mild and moderate forms. Under the conditions of a severe form of fluorosis, complete destruction of the prisms, fragmentation of the lamella, homogenization of areas on the entire enamel layer, which is due to the uneven distribution of acidic mucopolysaccharides, have been established. Morphologically and histochemically dystrophic changes in the areas of the affected enamel are confirmed by uneven distribution and accumulation of acidic glycosaminoglycans. An assessment of the effect of fluoride intoxication on the state of tooth enamel was carried out, which will allow to expand the possibilities of preventive measures for related specialists, as well as to create and develop additional treatment methods that will contribute to the improvement of physical and aesthetic indicators of teeth. dental health.

Microhardness Measurements on Tooth and Alveolar Bone in Rodent Oral Disease Models.

The mechanical property, microhardness, is evaluated in dental enamel, dentin, and bone in oral disease models, including dental fluorosis and periodontitis. Micro-CT (µCT) provides 3D imaging information (volume and mineral density) and scanning electron microscopy (SEM) produces microstructure images (enamel prism and bone lacuna-canalicular). Complementarily to structural analysis by µCT and SEM, microhardness is one of the informative parameters to evaluate how structural changes alter mechanical properties. Despite being a useful parameter, studies on microhardness of alveolar bone in oral diseases are limited. To date, divergent microhardness measurement methods have been reported. Since microhardness values vary depending on the sample preparation (polishing and flat surface) and indentation sites, diverse protocols can cause discrepancies among studies. Standardization of the microhardness protocol is essential for consistent and accurate evaluation in oral disease models. In the present study, we demonstrate a standardized protocol for microhardness analysis in tooth and alveolar bone. Specimens used are as follows: for the dental fluorosis model, incisors were collected from mice treated with/without fluoride-containing water for 6 weeks; for ligature-induced periodontal bone resorption (L-PBR) model, alveolar bones with periodontal bone resorption were collected from mice ligated on the maxillary 2nd molar. At 2 weeks after the ligation, the maxilla was collected. Vickers hardness was analyzed in these specimens according to the standardized protocol. The protocol provides detailed materials and methods for resin embedding, serial polishing, and indentation sites for incisors and alveolar. To the best of our knowledge, this is the first standardized microhardness protocol to evaluate the mechanical properties of tooth and alveolar bone in rodent oral disease models.

The effects of re-irradiation on the chemical and morphological properties of permanent teeth.

This study aimed to assess the in vitro effects of re-irradiation on enamel and dentin properties, simulating head and neck cancer radiotherapy retreatment. Forty-five human permanent molars were classified into five groups: non-irradiated; irradiated 60Gy, and re-irradiated with doses of 30, 40, and 50Gy. Raman spectroscopy, scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS) were employed for analysis. Raman spectroscopy assessed intensity, spectral area, and specific peaks comparatively. Statistical analysis involved Kolmogorov-Smirnov and One-Way ANOVA tests, with Tukey's post-test (significance level set at 5%). Significant changes in irradiated, non-irradiated, and re-irradiated enamel peaks were observed, including phosphate (438nm), hydroxyapatite (582nm), phosphate (960nm), and carbonate (1070nm) (p < 0.05). Re-irradiation affected the entire tooth (p > 0.05), leading to interprismatic region degradation, enamel prism destruction, and hydroxyapatite crystal damage. Dentin exhibited tubule obliteration, crack formation, and progressive collagen fiber fragmentation. EDX revealed increased oxygen percentage and decreased phosphorus and calcium post-reirradiation. It is concluded that chemical and morphological changes in irradiated permanent teeth were dose-dependent, exacerbated by re-irradiation, causing substantial damage in enamel and dentin.

Rapid Deposition of the Biomimetic Hydroxyapatite-Polydopamine-Amino Acid Composite Layers onto the Natural Enamel.

In this work, we developed a technology that enables rapid deposition of biomimetic composite films onto natural enamel slices (known as biotemplates). These films are composed of polydopamine (PDA) and nanocrystalline carbonate-substituted hydroxyapatite (nano-cHAp) that have been functionalized with amino acid l-Arginine. We utilized atomic force microscopy (AFM) and scattering scanning near-field optical microscopy (s-SNOM) combined with infrared (IR) synchrotron to achieve nanoscale spatial resolution for both IR absorption and topography analyses. This combined analytical modality allowed us to understand how morphology connects to local changes in the chemical environment on the biotemplate surface during the deposition of the bioinspired coating. Our findings revealed that when using the proposed technology and after the deposition of the first PDA layer, the film formed on the enamel surface nearly covers the entire surface of the specimen whose thickness is larger on the surface of the emerging enamel prisms. Calculation of the crystallinity index for the biomimetic layer showed a multiple increase compared with natural enamel. This indicates regular and dense aggregation of nano-cHAp into larger crystals, imitating the morphology of natural enamel rods. The microhardness of the formed PDA-based biomimetic layer mineralized with nano-cHAp functionalized with amino acid l-Arginine deposited on natural enamel was practically the same as that of natural enamel. The characterization of nano-cHAp-amino acid-PDA layers using IR and Raman microspectroscopy showed that l-arginine acts as a conjunction agent in the formation of mineralized biomimetic composite coatings. The uniformity of the mechanisms of PDA layer formation under different deposition conditions and substrate types allows for the formation of coatings regardless of the macro- and micromorphology of the template. Therefore, the results obtained in this work have a high potential for future clinical applications in dental practice.

Tissue Interactions in Dense Tissues of the Orofacial Region in Patients with Connective Tissue Dysplasia.

This study aimed to investigate the rate and quality of maturation of the mineral component of impacted teeth 38 and 48 and a fragment of the human lower jaw with connective tissue dysplasia (CTD) in different periods of postnatal ontogenesis. The study involved 102 males (76 with CTD and 26 without CTD), divided into age groups: 31-40, 41-50 and 51-60 years. For medical reasons, teeth 38 and 48 were removed from each patient, as well as a fragment of the alveolar part of the lower jaw in the projection of teeth 38 and 48 measuring 0.5 × 0.5 cm. The odontological parameters, the mineral density of the enamel and the lower jaw, the length and width of the enamel prisms, the spatial organisation of collagen fibrils and the dimensions of the bone plates of the lower jaw were determined. A decrease in optical density was observed at the age of 41-50 and 51-60 years with dysplasia, which indicated a decrease in mineral density and the presence of total areas of hypomineralisation relative to the age of 31-40 years. In the age groups of 41-50 and 51-60 years, pronounced sclerosis and deformation of the delimiting elements were observed at the border of the connective tissue structures and the periosteum. At the age of 31-40 years, the level of stratification of the bone plates was local; after 40 years, it was generalised. Progressive osteoporosis of the lower jaw and incomplete amelogenesis are obstacles to the correct and harmonious eruption of the lower 'wisdom' teeth after 30 years.

Options for processing enamel before manufacturing an adhesive splinting structure

Relevance. The durability of a splint depends on a number of factors: the level of oral hygiene, the degree of tooth mobility, the presence of occlusal trauma, and the strength of adhesion of the splint-dental interface. In turn, the issues of adhesion are inextricably linked to the anatomical features of the structure of hard tissue, particularly enamel. The correct execution of the cleaning, removal of the aprismatic layer and acid etching steps in the fabrication of an extracoronal splint determines the quality of adhesion at the tire-tooth interface.The aim of the study is to study the enamel surface structure in preparation for extracoronal splinting of teeth.Material and research methods. The 40 teeth were divided into 4 groups depending on the chosen method of preparation for fixation of the reinforcement structure in the extracoronal splint: brushing with paste, treatment with air-abrasive and ultrasonic methods, preparation with a fine-dispersed diamond boron.Results of the study. The preparation of enamel surface with fine diamond boron with particle size of 20 µm and acid etching with 37 % orthophosphoric acid determined a uniform character of microstructure, in the full volume the etched areas of enamel prisms amounted to 98.55±0.51 % of the total surface area of the treated enamel.Conclusion. The preparation of the enamel surface with a fine diamond boron removes the aprismatic layer, ensuring the longevity of the fabricated splint by creating a high-quality "hybrid" layer at the splint-dental interface.

AMELX gene association to early childhood caries in south-Indian children: a case-control study.

Genetic variants of AMELX gene can affect the protein content, organization of enamel prisms, microstructure and microhardness of the enamel, thus altering the caries susceptibility. The present study aims to assess the association between polymorphisms rs17878486, rs5934997, and rs5933871 of AMELX gene and Early Childhood Caries (ECC). This case-control study was conducted on 200 participants, aged 3-6years, with 100 controls and 100 children with ECC. A questionnaire was used to collect demographic data, birth-weight, type of delivery, oral hygiene practices, feeding history and 24-h diet diary. DNA was isolated from blood and subjected to PCR followed by Sanger sequencing. The CC genotype of rs17878486 showed an OR of 1.93 (0.34-10.81; P = 0.73). In a recessive model, the CC genotype of rs17878486 reported an OR of 2.04 (0.36-11.40; P = 0.68); rs5593871 reported an OR of 1.00 (0.31-3.21). Statistically significant differences (P ≤ 0.05) between genotype and allele frequencies of rs17878486, rs5934997, and rs5933871 were not observed between children with ECC and the controls. Polymorphisms of AMELX gene did not show a significant association with ECC in this population. However, documentation of genetic data in a global context of ECC may be essential for the future.

Molecular Evidence for Relaxed Selection on the Enamel Genes of Toothed Whales (Odontoceti) with Degenerative Enamel Phenotypes.

Different species of toothed whales (Odontoceti) exhibit a variety of tooth forms and enamel types. Some odontocetes have highly prismatic enamel with Hunter-Schreger bands, whereas enamel is vestigial or entirely lacking in other species. Different tooth forms and enamel types are associated with alternate feeding strategies that range from biting and grasping prey with teeth in most oceanic and river dolphins to the suction feeding of softer prey items without the use of teeth in many beaked whales. At the molecular level, previous studies have documented inactivating mutations in the enamel-specific genes of some odontocete species that lack complex enamel. At a broader scale, however, it is unclear whether enamel complexity across the full diversity of extant Odontoceti correlates with the relative strength of purifying selection on enamel-specific genes. Here, we employ sequence alignments for seven enamel-specific genes (ACP4, AMBN, AMELX, AMTN, ENAM, KLK4, MMP20) in 62 odontocete species that are representative of all extant families. The sequences for 33 odontocete species were obtained from databases, and sequences for the remaining 29 species were newly generated for this study. We screened these alignments for inactivating mutations (e.g., frameshift indels) and provide a comprehensive catalog of these mutations in species with one or more inactivated enamel genes. Inactivating mutations are rare in Delphinidae (oceanic dolphins) and Platanistidae/Inioidea (river dolphins) that have higher enamel complexity scores. By contrast, mutations are much more numerous in clades such as Monodontidae (narwhal, beluga), Ziphiidae (beaked whales), Physeteroidea (sperm whales), and Phocoenidae (porpoises) that are characterized by simpler enamel or even enamelless teeth. Further, several higher-level taxa (e.g., Hyperoodon, Kogiidae, Monodontidae) possess shared inactivating mutations in one or more enamel genes, which suggests loss of function of these genes in the common ancestor of each clade. We also performed selection (dN/dS) analyses on a concatenation of these genes and used linear regression and Spearman's rank-order correlation to test for correlations between enamel complexity and two different measures of selection intensity (# of inactivating mutations per million years, dN/dS values). Selection analyses revealed that relaxed purifying selection is especially prominent in physeteroids, monodontids, and phocoenids. Linear regressions and correlation analyses revealed a strong negative correlation between selective pressure (dN/dS values) and enamel complexity. Stronger purifying selection (low dN/dS) is found on branches with more complex enamel and weaker purifying selection (higher dN/dS) occurs on branches with less complex enamel or enamelless teeth. As odontocetes diversified into a variety of feeding modes, in particular, the suction capture of prey, a reduced reliance on the dentition for prey capture resulted in the relaxed selection of genes that are critical to enamel development.

Variation in enamel prism size in primate molars

ObjectiveThis study examines whether larger enamel prism diameters accommodate a greater enamel volume from the enamel-dentine junction (EDJ) to the outer-enamel surface (OES) in primate molars, and how prism size relates to enamel thickness and crown location. DesignWe assessed variation in enamel prism diameter in relation to crown location and enamel thickness in catarrhine lower molars (n = 14 species) and one platyrrhine. Prism diameter and enamel thickness were recorded in four locations (lingual lateral; lingual cuspal; buccal cuspal; buccal lateral), using a buccal-lingual section through the centre of the mesial cusps. Ten prism diameter readings were collected at inner (near the EDJ), outer (near the OES) and middle (between the two locations) enamel for each location. ResultsMean prism diameter values for each species were similar (range: 4.06 µm to 5.81 µm). Prism diameter enlarged from inner to outer enamel, suggesting larger prisms help accommodate the increase in enamel volume from the EDJ to the OES. Average prism diameter does not associate with enamel thickness. Instead, cuspal positions had significantly smaller prism diameter at the EDJ than lateral positions, and larger prism sizes at the OES, leading to an overall similar prism diameter mean for all positions (Lingual lateral: 5.11 µm; Lingual cuspal: 5.04 µm; Buccal cuspal: 4.78 µm; Buccal lateral: 4.99 µm). ConclusionsOur study revealed consistent average enamel prism diameters in various crown locations of lower primate molars, potentially contributing to the mechanical integrity and functional optimization of enamel in primates.

Case Repor Case Report and X t and X-ray Microtomography and Scanning Electr aphy and Scanning Electron Microscopy Analysis of Teeth with Hypocalcified Amelogenesis Imperfecta

Amelogenesis imperfecta (AI) is a genetic disease characterized by producing morphological and structural changes in tooth enamel. Objective: To highlight the morphological changes observed in teeth with hypocalcified AI based on scanning electron microscopy and microtomography analysis. Case report: An adult male had teeth seriously compromised by hypocalcified AI. The treatment plan involved removal of third molars followed by restorative and prosthetic treatment. After extraction, the teeth were analyzed by SEM and X-ray microtomography (microCT). Teeth with AI revealed the presence of microfractures arranged from the outer surface to the center of the enamel. Microfractures had a cracked or “cracked ground” pattern. SEM confirmed the presence of microfractures and distortion in the orientation of the enamel prisms in some regions. Conclusion: Teeth of patients with hypocalcified amelogenesis imperfecta IIIA subtype show significant structural changes that are closely related with the ease of fractures.

A novel image processing procedure for the quantitative evaluation of dental enamel prism arrangement.

Enamel prism is the main microstructural unit of mammalian enamel which composed of hundreds of bioapatite nanocrystals. Prism structure plays a key role in the excellent mechanical performance of dental enamel during millions of chewing cycles without significant remodeling. Thus, quantitative understanding of prism architecture is of utmost importance for biomechanical materials design. To characterize enamel prism orientation quantitatively, a novel image processing method has been developed. Our method is based on scanning electron microscopy images of etched enamel surface and consists of an ellipse fitting procedure, which provides a numerical approximation of prism shape and orientation in the studied cross section. The obtained analytical data allow to construct color coded orientation maps, which provide quick and useful insight into the microstructure of enamel. Besides striking visualization, orientation maps allow to extract and plot the rich information on the azimuthal and inclination angles of the prisms as function of location. Numerical data on prism arrangement can be analyzed using statistical tools over large areas, which paves the way towards quantifying comparative investigation of prism arrangement either in dentistry research or evolution biology. The application of the method is demonstrated for a distal-mesial cross-section of sound human tooth enamel. HIGHLIGHTS: Scanning electron microscopy images of etched enamel surface are analyzed using ellipse fitting. Geometrical parameters of the fitted ellipses provide numerical data of thousands of prisms. Prism arrangement is visualized on color coded orientation maps and analyzed using statistical tools.

How mangabey molar form differs under routine vs. fallback hard-object feeding regimes

Background Components of diet known as fallback foods are argued to be critical in shaping primate dental anatomy. Such foods of low(er) nutritional quality are often non-preferred, mechanically challenging resources that species resort to during ecological crunch periods. An oft-cited example of the importance of dietary fallbacks in shaping primate anatomy is the grey-cheeked mangabey Lophocebus albigena. This species relies upon hard seeds only when softer, preferred resources are not available, a fact which has been linked to its thick dental enamel. Another mangabey species with thick enamel, the sooty mangabey Cercocebus atys, processes a mechanically challenging food year-round. That the two mangabey species are both thickly-enameled suggests that both fallback and routine consumption of hard foods are associated with the same anatomical feature, complicating interpretations of thick enamel in the fossil record. We anticipated that aspects of enamel other than its thickness might differ between Cercocebus atys and Lophocebus albigena. We hypothesized that to function adequately under a dietary regime of routine hard-object feeding, the molars of Cercocebus atys would be more fracture and wear resistant than those of Lophocebus albigena. Methods Here we investigated critical fracture loads, nanomechanical properties of enamel, and enamel decussation in Cercocebus atys and Lophocebus albigena. Molars of Cercopithecus, a genus not associated with hard-object feeding, were included for comparison. Critical loads were estimated using measurements from 2D µCT slices of upper and lower molars. Nanomechanical properties (by nanoindentation) and decussation of enamel prisms (by SEM-imaging) in trigon basins of one upper second molar per taxon were compared. Results Protocone and protoconid critical fracture loads were significantly greater in Cercocebus atys than Lophocebus albigena and greater in both than in Cercopithecus. Elastic modulus, hardness, and elasticity index in most regions of the crown were greater in Cercocebus atys than in the other two taxa, with the greatest difference in the outer enamel. All taxa had decussated enamel, but that of Cercocebus atys uniquely exhibited a bundle of transversely oriented prisms cervical to the radial enamel. Quantitative comparison of in-plane and out-of-plane prism angles suggests that decussation in trigon basin enamel is more complex in Cercocebus atys than it is in either Lophocebus albigena or Cercopithecus cephus. These findings suggest that Cercocebus atys molars are more fracture and wear resistant than those of Lophocebus albigena and Cercopithecus. Recognition of these differences between Cercocebus atys and Lophocebus albigena molars sharpens our understanding of associations between hard-object feeding and dental anatomy under conditions of routine vs. fallback hard-object feeding and provides a basis for dietary inference in fossil primates, including hominins.

Gradient structural anisotropy of dental enamel is optimized for enhanced mechanical behaviour

Exceptional mechanical performance of dental enamel in the harsh environment of oral cavity can be preserved on decade timescale, which is a unique property in comparison with functional nanomaterials. Hierarchic architecture of enamel, based on site-specific structural organization of apatite nanocrystals has a key role in this durability.In the present study, a novel SEM imaging based method is presented for obtaining quantitative information on enamel prism orientation in sound primary dental enamel. This missing puzzle of quantification of the hierarchical enamel structure, along with spatial mechanical and chemical mapping, shed light on the optimum anisotropic gradient behaviour of elastic modulus of dental enamel.Specifically, orientation and composition dependent contributions in both the spatially changing hardness and elastic modulus were separated. Anisotropy of the enamel’s modulus was predicted and verified by the spatial variation of average prism orientation. Based on our results we conclude that the anisotropy of modulus for the bulk enamel arises from the elastic gradient in direction normal to the enamel external surface combined with the nearly constant value of modulus in the perpendicular cross section. This behaviour results in high surface strength and additionally can be responsible to the superior durability of human enamel.

MORPHOLOGICAL FEATURES OF DENTAL TISSUES IN STREPTOZOTOCIN-INDUCED DIABETES MELLITUS MODEL

The global issue of diabetes mellitus (DM), which is a serious burden faced by the healthcare systems and economies in many countries, has been increasing steadily in the recent decades. The fast pace of DM growth and prevalence, as well as associated complications (macro- and microangiopathy, neuropathy, nephropathy, impaired vision), high economic costs and social damage, high disability and mortality rates entailed by this disease take constant improvement of the respective diagnostics, prevention and treatment approaches. Dental manifestations of DM are diagnosed in most patients and reveal themselves through demineralized hard dental tissues, high intensity of dental caries and its prevalence, as well as the prevalence of periodontal diseases and issues affecting the oral mucosa. Our research included 60 male Wistar stock rats, all divided into two groups: the comparison group with no DM (n=10) and the main group with induced DM (n=50). DM modeling was done by a single intraperitoneal injection of streptozotocin (dosage – 65 mg/kg). The main group lab animals were removed from the experiment on Days 8, 16, 24, 32 and 60 under anesthesia by decapitation. All the histological and morphometric changes observed in the dental tissues were recorded in the ImadgeJ software package using a Leica DM2500 hardware and software set. The studied sections were used to evaluate the thickness of enamel, dentin, predentin, cement, pulp, the dentin tubule diameter, as well as the density of odontoblasts and ameloblasts. On Day 60 into the experiment, the following changes were identified in relation to the hard dental tissues: regarding the enamel − demineralization, disintegration of the interprism substance; deformed enamel prisms; erosion-type defects developing; regarding the dentin − expanded dentin tubules, vacuole dystrophy of odontoblasts, accumulating edematous fluid under the odontoblast layer, deformation and atrophy of odontoblasts; regarding the cement – layer thinning, cementolysis, cavities developing. Quantitative evaluation of rat dental tissues on Day 60, if compared with intact animals, revealed a multidirectional dynamics in the morphometric values. There was a statistically significant (p≤0.05) decrease in the enamel thickness identified (from 31.06±2.17 microns to 18.19±1.36 microns), in predentin (from 25.19±1.48 microns to 20.93±1.16 microns), in cement (from 37.28±2.04 microns to 31.04±1.46 microns), in the dentin tubule diameter (from 1.82±0.14 microns to 1.56±0.13 microns), as well as in the density of odontoblasts (from 7683.24±319.76 units/mm2 to 7312.61±256.19 units/mm2) along with a statistically reliable (p ≤0.05) increase in the thickness of dentin (from 96.54±3.39 microns to 105.11± 3.16 microns), pulp (from 107.43± 4.12 microns to 120.38±5.26 microns), as well as in the ameloblast density (from 6471.39± 272.18 units/mm2 to 6849.06±253.84 units/mm2). The outcomes expand the understanding of the structural changes affecting rat dental tissues at various times through modeling of Type 1 diabetes, as well as results could be used for developing pharmacological correction methods aiming at the reduction of the pathology intensity.

The Effect of Bonding Strategy and Aging on Adhesion to Primary Enamel: An In-Vitro Study.

Resin composites are commonly used in pediatric dentistry, but there is limited evidence on adhesion to primary teeth, especially primary enamel. In this study, three bonding strategies were assessed - one-step self-etch (1-SE), two-step self-etch (2-SE), and three-step etch-and-rinse (3-ER) - by measuring the immediate and aged microshear bond strength (µSBS) to sound primary enamel. 120 extracted human primary molars with sound buccal surfaces were used for µSBS testing. Six adhesive protocols (two per bonding strategy) were selected and µSBS was measured either after 24 h or 10,000 thermal cycles (n = 10). Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) were used to determine failure modes. Furthermore, 18 primary molars were etched using the different adhesive protocols (n = 3) for the measurement of surface roughness (Sa) using CLSM and morphological analysis using SEM. After 24 h, there was no significant difference in µSBS between 1-SE and 2-SE strategies (p = 0.96), but the 2-SE strategy yielded significantly higher µSBS after thermocycling (p < 0.001). The highest µSBS was obtained using the 3-ER strategy regardless of aging (p < 0.001). The 3-ER strategy clearly exposed enamel prisms and resulted in the highest Sa (p < 0.001). In contrast, if SE strategies were used, enamel prisms were barely recognizable, and Sa was not significantly different from baseline (p > 0.95). The 3-ER strategy is optimal for bonding to primary enamel. The etching effect of SE strategies is weaker, resulting in lower µSBS. Thermocycling revealed that the bonding durability of the 1-SE strategy is inferior to that of to multi-step strategies.